The polymerisation of olefins by bringing them into contact with a catalyst system in a reactor system comprising a slurry phase reactor is known. In a typical slurry phase polymerisation process a slurry of polymer solids in a liquid diluent is circulated in a loop reactor to which fresh catalyst and reactants are added, and from which is withdrawn a slurry of polymer solids in the diluent.
Polymerisation is generally performed continuously; although the catalyst system and make-up reactants may be introduced into the reactor continuously or discontinuously as required. The polymer produced may also be withdrawn from the reactor either continuously or discontinuously as required.
The polymer produced is withdrawn as slurry of polymer solids in the diluent. The diluent and other reaction components therein are separated from the polymer solids, and recycled to the reactor.
Cooling of the reactor is necessary to remove the exothermic heat of reaction. In a loop reactor this is achieved by flowing a cooling fluid, generally water, through jackets disposed about the legs of the reactor.
The polymerisation of olefins by bringing them into contact with a catalyst system in a reactor system comprising a gas phase reactor is also known. In a fluidised bed gas phase polymerisation process, for example, a bed of polymer is maintained in a fluidised state by an ascending stream of fluidisation gas comprising the olefin, which gas exits the reactor and is then recycled.
The start-up of the polymerisation reaction in the gas phase is generally performed by introducing a pre-formed bed of polymer, known as a seedbed, to the reactor, fluidising this seedbed and forming a reaction gas mixture in the reactor, and then introducing a catalyst to initiate reaction.
Polymerisation may then be performed continuously; the catalyst system and make-up reactants and other reaction gas mixture components being introduced into the reactor continuously or discontinuously as required. The polymer produced may be withdrawn from the reactor either continuously or discontinuously. The pre-formed seedbed forms the initial fluidised bed but as reaction takes place and polymer solids are withdrawn this is eventually replaced by a bed of the formed polymer.
The gas leaving the reactor is generally cooled before being recycled back to the reactor. In preferred processes it is cooled below a temperature at which liquid components condense out of the gas stream, and both the liquid and gaseous phases are recycled, wherein the vaporisation of the condensed liquid components in the reactor provides significant cooling to the reaction. The formation of condensed liquid from the gas exiting the reactor and the introduction of this condensed liquid into the reactor is generally known as “condensed mode” operation.
Numerous components can be added to the reaction during polymerisation. Obviously, monomers, and any comonomers, and catalyst have to be added to replace consumed components, but other components, such as hydrogen, activators and antistatic agents may also be added at various times.
It is known to introduce components to the reactor at multiple locations within a reactor.